1. Field of the Invention
The present invention relates to heat-and-power engineering at metallurgical enterprises and, more particularly, to the design of tubular cooled members for a continuous furnace, said members being fitted with an evaporative cooling plant.
2. Description of the Prior Art
There is known in the art tubular cooled members of a metallurgical furnace, which comprises straight cooled pipes representing a supporting structure made up of long-length (up to 25 m) horizontal sections of a relatively large diameter (with an inside diameter of up to 200 mm). Accommodated coaxially in the interior of said pipes (if they are over 90 mm in diameter) are inserts (metallic rods or plugged tubes), which makes it possible to reduce the flow rate of a circulating coolant (the amount of coolant flowing through a cross-sectional area of said tubular cooled member per unit time) and to improve the cooling conditions of said pipes. In the prior-art construction a gap between the outside surface of the insert and the inside surface of the pipe in which said insert is accommodated remains the same throughout the pipe length.
However, a major problem encountered in providing the serviceability of said horizontal pipes in case of evaporation cooling is that it precludes the stratification of the coolant flow in the surface boiling zone when the fluid is subcooled, and in the zone where the boiling process is initiated, as well as in ruling out the overheating of the top generatrix of said pipes.
Since the rate of circulation is the main criterion of reliable cooling of said horizontal pipe sections and the allowable rates of circulation for the first and last sections of said pipes differ in value, it turns out that, with a constant gap between the outside surface of the insert and the inside surface of the pipe in which said insert is accommodated, the rate of circulation for the last pipe section is much greater than its allowable value, which is determined by the optimum values of pressure loss. This is evidenced by a reduction in the allowable rate of circulation stemming from an ever-growing rate of coolant flow moving along the tubular cooled member due to an increase in the vapour content under a higher total heat load. This gives rise to an undue hydraulic resistance, does not allow the requisite circulation rates to be provided at the beginning of the tubular cooled member and adversely affects the cooling efficiency.
In establishing circulation circuits with the total heat loads approximating each other, the straight cooled pipes forming a tubular cooled member are coupled in pairs with a bent connecting pipe.
The aforesaid inserts were introduced only into the straight pipe sections. This non-continuous arrangement of the inserts caused disturbances in the dynamics of the coolant flow in the transition section, i.e. in the place where the coolant passes from said straight pipe into the bent connecting pipe, the top part of said bent connecting pipe being damaged as a result.
The use of bent connecting pipes with diminishing cross-sections made it possible to decrease, but did not completely eliminate, these failures in view of the possibility of plugging the cross-section of said bent connecting pipe, if the insert is shifted to some extent, and because of the presence of said transition section between the straight and bent connecting pipes, the cross-section of said transition section substantially exceeding that of the bent connecting pipe.
Another disadvantage of the prior-art construction lies in the provision of a great number of welded joints which must meet exacting requirements as to their quality (at a pressure in the cooling system of up to 45 atm and considerable dynamic loads).
In view of the above disadvantages it was not always possible to insure the requisite rate of the coolant circulation. As for the failure of the tubular cooled members that took place in the course of operation of said cooling plants, for the most part they occured in the first horizontal sections in the zone of the top generatrix of the pipe. Characteristic of the damaged places were the thinning and distortion (bulging) of the pipe walls and the appearance of through holes which were indicative of a vapour phase corrosion attack resulting from overheating due to an inadequate coolant circulation rate.